Video signal frequency modulator having automatic control function and controlling method therefor

Abstract

A video signal frequency modulator having an automatic control function includes a reference generator for generating a sync tip level signal and a white peak level signal, a first switch for selecting one of the sync tip level signal, white peak level signal or a clamped video signal according to a mode control signal, a variable gain amplifier for amplifying the output of the first switch to a predetermined gain and converting the amplified result into a current, an adder for adding the output of the variable gain amplifier with a predetermined set value, an oscillator for frequency-modulating the output of the adder, a frequency detector for shaping and frequency-dividing the output of the oscillator, a microcomputer for comparing the output of the frequency detector with a predetermined reference frequency and outputting first and second control data and the mode control signal, a carrier frequency setting portion for controlling the magnitude of the predetermined set value according to the first control data, and a frequency deviation setting portion for controlling the predetermined gain according to the second control data.

What is claimed is: 
     
       1. A signal frequency modulator which, in a first control mode, controls a carrier frequency using a first reference signal, in a second control mode, controls a frequency deviation with a second reference signal, and in a normal mode, modulates the frequency of a video signal to be modulated, comprising: a reference signal generator for generating a first reference signal and a second reference signal;   a first switch for selecting one of said first reference signal, said second reference signal and said video signal according to a mode control signal;   a variable gain amplifier for amplifying the selected signal to a predetermined gain and converting the amplified signal into a current signal;   an adder for adding the output of said variable gain amplifier to a predetermined set value;   an oscillator for frequency-modulating the output of said adder;   a frequency detector for shaping and frequency-dividing the output of said oscillator;   a microcomputer for comparing the output of said frequency detector with a predetermined reference frequency and outputting first and second control data and said mode control signal;   a bus decoder for receiving, latching and storing, and transmitting said first and second control data;   carrier frequency setting means for controlling the magnitude of said predetermined set value according to said first control data; and   frequency deviation setting means for controlling said predetermined gain according to said second control data.   
     
     
       2. The signal modulator of claim 1, wherein said video signal to be modulated is a video luminance signal, said first reference signal is a sync tip level signal, and said second reference signal is a white peak level signal. 
     
     
       3. The signal frequency modulator of claim 1, further comprising a second switch for connecting or disconnecting said frequency detector and said oscillator according to said mode control signal. 
     
     
       4. The signal frequency modulator of claim 1, wherein said frequency detector comprises a Schmitt trigger circuit for waveform-shaping said oscillator output and a divider for frequency-dividing the output of said Schmitt trigger circuit. 
     
     
       5. The signal frequency modulator of claim 1, wherein said carrier frequency setting means comprises a digital-to-analog converter for converting said first control data into an analog signal, and a voltage to current converter for converting said analog signal into a current signal. 
     
     
       6. The signal frequency modulator of claim 1, wherein said frequency deviation setting means comprises a digital-to-analog converter for converting said second control data into an analog signal. 
     
     
       7. The signal frequency modulator of claim 1, wherein said bus decoder is capable of storing said first and second control data for an indefinite duration which is at least greater than a frame period of said video signal. 
     
     
       8. A frequency modulator for frequency-modulating a video signal to be modulated, comprising: a reference signal generator for generating a first reference signal and a second reference signal;   a first switch for selecting one of said first reference signal, said second reference signal and said video signal to be modulated according to a mode control signal;   a variable gain amplifier for amplifying the selected signal to a predetermined gain and converting the amplified signal into a current signal;   an adder for generating an added signal by adding said current signal to a predetermined set value;   an oscillator for frequency-modulating said added signal;   a Schmitt trigger circuit for shaping said frequency-modulated added signal;   a divider for frequency-dividing the shaped signal;   a microcomputer for comparing the output of said divider with a predetermined reference frequency and generating first and second control data and said mode control signal;   a bus decoder for receiving, latching and storing, and transmitting said first and second control data, and said mode control signal;   a first digital-to-analog converter for converting said first control data into a first analog signal;   a second digital-to-analog converter for converting said second control data into a second analog signal for controlling said predetermined gain according to said second control data; and   a V/I converter for converting said first analog signal into a current signal for controlling the magnitude of said predetermined set value according to said first control data.   
     
     
       9. The frequency modulator of claim 8, wherein said video signal to be modulated is a clamped video signal, said first reference signal is a sync tip signal, and said second reference signal is a white peak signal. 
     
     
       10. The frequency modulator of claim 7, wherein said bus decoder is capable of storing said first and second control data for an indefinite duration which is at least greater than a frame period of said video signal. 
     
     
       11. A method for adjusting a frequency modulator for modulating a video signal to be modulated, the method comprising the steps of: supplying a first reference signal to an amplifier;   converting the amplified first reference signal to a first current signal;   adding said first current signal to a predetermined set signal;   frequency modulating said first added signal;   supplying said first frequency-modulated signal to a microcomputer;   generating a first control data signal corresponding to the difference between the carrier frequency of said first frequency-modulated signal and a carrier reference frequency;   latching and storing said first control data signal;   adjusting said predetermined set signal in accordance with said first control data signal;   supplying a second reference signal to said amplifier;   converting the amplified second reference signal to a second current signal;   adding said second current signal to said predetermined set signal;   frequency modulating said second added signal;   supplying said second frequency-modulated signal to the microcomputer;   generating a second control data signal corresponding to the difference between the frequency deviation of said second frequency-modulated signal and a reference frequency deviation;   latching and storing said second control data signal; and   adjusting the gain of said amplifier in accordance with said second control data signal.   
     
     
       12. The method of claim 11, wherein said signal to be modulated is a video signal, said first reference signal is a sync tip level signal, and said second reference signal is a white peak signal. 
     
     
       13. The method of claim 12, wherein said step of adjusting said predetermined set signal comprises the steps of: converting said first control data into a first analog control signal;   converting said first analog control signal to a first current control signal; and   supplying said first current control signal as said predetermined set signal.   
     
     
       14. method of claim 13, wherein said step of adjusting the gain of said amplifier comprises the steps of: converting said second control data signal to a second analog control signal; and   supplying said second analog control signal to said amplifier to adjust said gain.   
     
     
       15. The method of claim 9, wherein said steps of latching and storing said first and second control data signals are both performed so as to store said first and second control data signals for an indefinite duration which is at least greater than a frame period of said signal to be modulated.